Nanochemistry: Creating Chemical Systems with Unique Effects

1.1 Definition

Nanochemistry is concerned with generating and altering chemical systems, which develop special and often new effects as a result of the laws of the nanoworld. The bases for these are chemically active nanometric units such as supramolecules or nanocrystals. Nanochemistry looks set to make a great deal of progress for a large number of industry sectors. Nanotechnology exists in the realm where many scientific disciplines meet. Achievements in physics are getting progressively smaller – from valves to electronics, down to microelectronics and quantum computing.

It mirrors the downsizing in focus in the biological sciences, from cells to genomics. Conversely, achievements in chemistry have been converging into the nanometre range from below – from atoms and molecules to supramolecular chemistry.

Nanochemisty focuses on the unique properties of materials in the 1–100 nm scale. The physical, chemical, electrical, optical and magnetic properties of these materialsare all significantly different from both the properties of the individual building blocks (individual atoms or molecules), and also from the bulk materials.

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Nanochemistry is a truly multidisciplinary field, forming a bridge between nanotechnology and biotechnology, spanning the physical and life sciences. The Nanochemistry Research Institute (NRI) at Curtin carries out world-class research to provide innovative solutions to

- energy and resources
- materials and manufacturing
- electronics
- agricultural
- environmental management, and
- health and medical industries

Nanochemistry applications in the materials, resources and energy sectors range from the design of crystalline catalysts and the control of crystal size, morphology, phase and purity, to the design and use of additives to control crystallization and inhibit scale formation.

In the biological field, control of chemistry at the supramolecular level can lead to the development of a wide variety of new and improved biomaterials, such as artificial bones and tissues, as well as new pharmaceuticals and improved methods of drug delivery.1

ENGINEERING, SCIENCE

‘‘We are like dwarfs on the shoulders of giants, so that we can see more than they.’’ Bernard of Chartres, 12th century with nanoscience being the discipline concerned with making, manipulating and imaging materials having at least one spatial dimension in the size range 1–1000 nm and nanotechnology being a device or machine, product or process, based upon individual or multiple integrated nanoscale components, then what is nanochemistry?

In its broadest terms, the de.ning feature of nanochemistry is the utilization of synthetic chemistry to make nanoscale building blocks of different size and shape, composition and surface structure, charge and functionality. These building blocks may be useful in their own right. Or in a self-assembly construction process, spontaneous, directed by templates or guided by chemically or lithographically de.ned surface patterns, they may form architectures that perform an intelligent function and portend a particular use.2

1.2 Objective of nanochemistry

- Creating nanoparticles
- Allowing properties of nanosystems to evolve, manipulating and controlling them
- Encapsulating and transporting materials (e.g. deodorant with nanodroplets)4

1.3 Nanochemistry used in: -

- Cosmetics, e.g. sunscreen, toothpaste, skincare products
- Sanitary ware
- Built-in ovens and baking trays
- Gas-tight packaging
- Screens, photographic films
- Separating technology for waste water treatment and food production
- Catalysers for chemical reactions
- Exhaust purification5

It is also used in formation of :-

- Commercialization of nanochemicals
- Nanooxides of precious, ferromagnetic, rare metals (Ti, Zr etc.)

Nanopolymers and membranes
- Nanomaterials (cement, fertilizers)
- Nanopowders in chemical applications
- Nanogreen chemistry
- Nano energy applications
- Environmental applications of nanotechnology

When thinking about self-assembly of a targeted structure from the spontaneous organization of building blocks with dimensions that are beyond the sub-nanometer scale of most molecules or macromolecules, there are five prominent principles that need to be taken into consideration.

These are: (i) building blocks, scale, shape, surface structure, (ii) attractive and repulsive interactions between building blocks, equilibrium separation, (iii) reversible association–dissociation and/or adaptable motion of building blocks in assembly, lowest energy structure, (iv) building block interactions with solvents, interfaces, templates, (v) building-blocks dynamics, mass transport and agitation. A challenge for perfecting structures made by this kind of self-assembly chemistry is to .nd ways of synthesizing (bottom-up) or fabricating (top-down) building blocks not only with the right composition but also having the same size and shape. No matter which way building blocks are made they are never truly monodisperse, nless they happen to be single atoms or molecules.

There always exists a degree of polydispersity in their size and shape, which is manifest in the achievable degree of structural perfection of the assembly and the nature and population of defects in the assembled system. Equally demanding is to make building blocks with a particular surface structure, charge and functionality. Surface properties will control the interactions between building blocks as well as with their environment, which ultimately determines the geometry and distances at which building blocks come to equilibrium in a self-assembled system. Relative motion between building blocks facilitates collisions between them, whilst energetically allowed aggregation deaggregation processes and corrective movements of the self-assembled structure will allow it to attain the most stable form.

6 Providing the building blocks are not too strongly bound in the assembly it will be able to adjust to an orderly structure. If on the other hand the building blocks in the assembly are too strongly interacting, they will be unable to adjust their relative positions within the assembly and a less 1 ordered structure will result. Dynamic effects involving building blocks and assemblies can occur in the liquid phase, at an air/liquid or liquid/liquid interface, on the surface of a substrate or within a template co-assembly.

As this text describes, building blocks can be made out of most known organic, inorganic, polymeric, and hybrid materials. Creative ways of making spheres and cubes, sheets and discs, wires and tubes, rings and spirals, with nm to cm dimensions, abound in the materials self-assembly literature. They provide the basic construction modules for materials self-assembly over all scales, a new way of synthesizing electronic, optical, photonic, magnetic materials with hierarchical structures and complex form, which is the central theme running throughout this chapter. A .owchart describing these main ideas is shown in igure 1.

Nano-, a pre.x denoting a factor, its origin in the Greek nanos, meaning dwarf. The term is often associated with the time interval of a nanosecond, a billionth of a second, and the length scale of a nanometer, a billionth of a meter or 10 A ° . In its broadest terms, nanoscience and nanotechnology congers up visions of making, imaging, manipulating and utilizing things really small. Feynman’s prescient nano world ‘‘on the head of a pin’’ inspires scientists and technologists to venture into this uncharted nano-terrain to do something big with something small.7

1.4 Large and Small Nanomaterials

It was not so long ago in the world of molecules and materials that 1 nm (1 nm ¼ 10 A ° ) was considered large in chemistry while 1 m m (1 m m ¼ 1000 nm ¼ 10,000 A ° ) was considered small in engineering physics. Matter residing in the ‘‘fuzzy interface’’ between these large and small extremes of length scales emerged as the science of nanoscale materials and has grown into one of the most exciting and vibrant fields of endeavor, showing all the signs of having a revolutionary impact on materials as we know them today. In our time, ‘‘nano’’ has left the science reservation and entered the industrial technology consciousness and public and political perception.

Indeed, bulk materials can be remodeled through bottom-up synthetic chemistry and top-down engineering physics strategies as nanomaterials in two main ways, the first by reducing one or more of their physical dimensions to the nanoscale and the second by providing them with nanoscale porosity. When talking about finely divided and porous forms of nanostructured matter, it is found that ‘‘nanomaterials characteristically exhibits physical and chemical properties different from the bulk as a consequence of having at least one spatial dimension in the size range of 1–1000 nm’’.